/diy/ - Do It Yourself

I got this cheap tube guitar preamp online. When I turn it on and plug in my headphones, there's a nasty buzz.
I know it's a cheap preamp and I shouldn't expect much, but this is well beyond unusable.
Assuming it's not the tube that's the issue, I suspect it's the grounding. It's made out of metal and when I put my hand on it, the buzz gets slightly quieter.

Do you think it's the grounding or the faulty tube? How would I go about tackling this besides complaining to the seller (already did).